The present disclosure relates to optical, or photonic, transport networks or systems and associated devices. An example of the present disclosure includes a fiber optic communication network and optical circuit components used in the network. More particularly, the present disclosure relates to optical transport system architectures and optical devices used in the optical transport system.
Fiber optical systems generally refer to the medium and technology associated with the transmission of signals in the form of light pulses, or photons, along a glass or plastic fiber. Optical systems are distinguishable from electrical systems using conventional electrically conductive wires, such as copper wire, in the transmission of electrical signals. Optical systems also include advantageous capabilities over electrical systems. For example, electrical signals interact with each other and their environment. This results in a need for non-intersecting and spaced-apart electrical wire links between electronic devices or electrical components. In contrast, photons generally do not interact with each other, and this leads to the possibility of different photonic signals sharing the same optical fiber.
Optical systems typically combine different photonic signals onto the same optical fiber, or separate photonic signals carried on the same optical fiber, with a generally similar basic circuit structure. Several optical transmitters can be used to each generate a particular optical signal. The optical signals from the transmitters are input to an optical multiplexer. The optical multiplexer is a photonic circuit component that combines several photonic signals into a single photonic transmission that can be carried on the single optical fiber. In order to separate the single photonic transmission on the single optical fiber, systems can use an optical de-multiplexer. The optical de-multiplexer is a photonic circuit component that separates a single photonic transmission into the individual photonic signals. The outputs of the optical de-multiplexer are coupled to optical receivers. Each of the individual photonic signals is carried on to the corresponding optical receiver.
In general, the multiplexer or de-multiplexer in the basic optical structure performs a type of wavelength division multiplexing, or WDM. Wavelength division multiplexing is used to carry many different types of data on the same optical fiber. Wavelength division multiplexing is a fiber optic technique that employs light wavelengths to transmit photonic signals in parallel on the same optical fiber. Wavelength division multiplexing has enabled optical service providers to meet consumer demands for ever-increasing bandwidth. Wavelength division multiplexing uses several to many channels (also known as lambdas or colors) to provide high capacity bandwidth across the optical system or optical network. Each channel carries an individual photonic signal providing the same bandwidth per channel in a single photonic stream. The channels are de-multiplexed at the end location. Several devices can be used to provide the multiplexing or de-multiplexing functions.
Often, systems using wavelength division multiplexing employ one of two general network topologies to manage the bidirectional transmission of data over a network. (Bidirectional data transmission occurs when signals are transmitted along both directions of an optical transmission path such as optical fiber.) These two topologies are a star and a ring. The star topology is where all of the data is transmitted to a central location of the network and then retransmitted to the intended recipient. An example can be imagined by considering a company mail room. Letters to be sent are first collected and brought to the mail room, and from there the letters are taken to the intended addressees. A ring topology is where all of the transmitters and recipients are linked together in a closed loop. An example can be imagined by considering the numbers on the face of an analog clock. If 1 wants to send a signal to 6, 1 must send the signal clockwise through 2-5 (or counterclockwise through 12-7). A third type of topology, a linear bus, is popular with many types of electronic systems, such as a personal computer, but is difficult to implement in optical systems.
Despite the popularity of the star and ring topologies, they are not without their disadvantages. In a star coupled network, all of the nodes are connected to a central location using optical transmission paths, and the central location broadcasts data from each transmitting node to generally all of the nodes on the network. In a passive star network, data is broadcast by splitting the optical signal. This results in a practical limitation of about sixteen nodes due to the reduction of power in the splitting process. An active star coupler regenerates the optical signal within the star and can be used for larger networks, but this requires significantly more controls, expense, and maintenance issues. Also, active stars typically employ the technologies and controls used in constructing a difficult-to-implement linear bus topology. A ring coupled network is more easily implemented and more scalable than the star network. Ring networks, however, are more dependent on each of the nodes. If one node fails, the entire communication network could be disrupted. In addition, the entire communication network could be disrupted if power fails, and the ring typically requires relatively large amounts of power to operate.
Accordingly, there is a continuing need for improved network topologies and devices used to support the network that conserve power, are scalable to accommodate a broad number of nodes, are easily maintained, and are readily implemented on optical systems where failure of a node or component does not disrupt a large portion of the network.